Antenna assembly



June 1953 F. J. LUNDBURG ETAL 2,640,930

7 ANTENNA ASSEMBLY Filed Jan. 12, 1950 r s Sheets-Sheet 1 INVENTORS i1 m/vx .2: w/vaaum gg' ATTORNEY June 2, 1953 F. J- LUNDBURG ETAL 2,640,930

I ANTENNA ASSEMBLY Filed Jan. 12, 1950 I 3 Sheets-Sheet 2 ATTORNEYJune2,l953 R LLUNDBURG ETAL :5 shets-sneet s INVENTORS FRANK J.LU/VDBU/PG FRH/VC/S X. BUCHER ATTCRNEY Patented June 2, 1953 UNITEDSTATES OFFICE FrankJ. Lundburg, East Orange, andFrancis-X'. Bucher,N'utley, N. J assignors; by mesneas signnients', to InternationalStandard Electric Corporation, New'York, Y1, as corporation of:

Delaware Applicationlanuary 12', 1950; Serial"No;.138;13'8

15 Claims; 1

This: invention" relates. to antennas and more particularly to anantenna assembly designed for providing, an omnidirectional and rotatingfigure-of-eight pattern.

Various systems. have been proposed for provi'ding'omnidirectional radiobeacons. In general these systemsmay comprise. a directive antennaproducing a. normal figure-of-eight pat-.- tern and an omnidirectionalantenna or radiator; the energy of which combined with thevdirectivefigure-of-eight pattern. will produce a unidirective pattern ofgenerally cardiodal form. If then the pattern is caused'to. rotate at agiven rate the" null pointof the. cardiod may be detented and thedirection line obtained thereby which may serve to guide. craft along agiven course'towardor away from. the beacon. In orchar that: a;continuous indication be provided. it is" necessary that rotation of thedirective pat.- tern be at: a fairly high. rate. mal frequencies usedfor navigation purposes the: directive antenna structure is. too largeto be readily rotatable at the required speed.

Furthermore. in most antenna systems, ale-- signed. for a singlepolarization, horizontal polar:- izati'on for example, there exists anaccompany.- i'ng; radiation polarized at right angles, thereto which"may cause errors in the directive. pattern produced in the receiving.arrangement. To

avoid the difficulty of rotating, large structures resort has been; madeto goniomet'ers. wherein. a coil is rotated in the field of energyproduced by two right angular fixed antenna. systems, so. that aneffective rotation of figure-of -eight' radiation pattern is provided.However, in such. a

casefith'ere' is present still certain errors introduced by thisexpedient.

It an object of our invention to provide. an antenna assembly for.omnidirectional, beacon usewh'erein the rotated directive. pattern is.produced by" the rotation of" a small antenna such as a dipole antennaunit.

This dipole is'made of' small dimensions relative to a half wave lengthatthe operating frequency, so that-it may be easily rotated and associated therewith, and is provided with a radiating structure toprovidethe desired omnidi rectional" pattern and resonator structure to furnishthe desired impedance characteristics.v of the system andto purify thepolarization.

According to a; feature of our invention a radio assemblyis providedcomprisinga dipole an.- tenna of small. length relative to a half wavelengthof the operating frequency, a resonator effectively open toradiation about the periphery Thus at the nor:-

2, of' the dipole and enclosing the antenna and an omnidirectionalantenna mounted symmetr-ically about the dipole radiator. The resonatoris in: the-form of a cage-made of conductive plates which may beinterconnected by vertical rods or maybe interconnected by a conductivesheet providedwitlr vertical slots around its periphery. Theomnidirectional radiator comprises radi'at-- ing elements arrangedsymmetrically about'the' dipole and cophasally' energized and may bepositioned' between adjacent rods or conductiveportionsofthe cage. The"resonator structure itself may producep'olarization errors of itsown andtoavoid these extensions may be provided;

" ascontinuous'conductive sheets or as cage structures of similarconstruction to the first one named, in the form of additional sectionsadded" either-above, or above and below the cage; further-toreducepolarization errors. The resona for" structure may not completelycompensate the capacitive reactance of the short dipole" so there maybe" provided within the first cage a second cage structure comprising aplurality of spaced rods 01'' a cylinder with a plurality of spacedslots about said dipole mounted on a di-- ameter smaller than the firstcage. On the rods of this smaller cage is arranged a conductive platewhich may be" adjusted to provide an inner. resonator of inductivereactance adjustable to the desired valueto compensate the capacitivereactance of the short dipole.

While we have set forth the principal objects and features of" ourinvention, a better under standingof the invention and more detaileddisclosure-of the objects and" features thereof may be had from theparticulardescription thereof made with reference to the accompanyingdrawing, in which:

Fig. 1" is an illustration of the physical construction of an entireassembly incorporating the features of our invention as viewed alonglinesl'lof Fig. 2, with certain of the elements omitted for clarityofillustration;

Fig. 21 is. a diagram more clearly illustrating the antenna constructionitself with respect to its functional operation;

Fig. 3 is a diagram illustrating the manner of. feeding theomnidirectional. antennas. of the assembly;

Figs. 4, 5,. and 6. arediagrammatic showings illustratinghow.polarizationerrors ariseand are compensated; and

Fig. '7. illustrates a modified physicalv construction of the, antennaassembly.

Referring to Fig. 1, a folded dipole unit 1 is illustrated which may befed by some form of feeding arrangement shown at 2 and may be coupledthrough a rotary coupler 3 to coaxial feed line 4. Adjacent the base ofthe coupler 2 is provided a first conductive plate 5 and spacedthere-above a second conductor plate 6. The

plates 5 and 6 are interconnected by a plurality of rods I, which formeffectively a resonator structure which may be considered as a radiatorexcited by dipole antenna I. Preferably the spacing between plates 5 and6 is made slightly greater than 2 at the center frequency. Rods I arespaced sufficiently close to one another around the periphery to providean effective vertical polarization screen or filter so that only thehorizontally polarized energy passes. Each two adjacent rods I formeffectively the boundaries of a short section of wave guide which act asthe ultimate radiators. As it is longer than a half wave length it willfreely pass radiated energy in the TE m mode. By its resonator actionthe resonator efiectively provides an impedance match with the outeratmosphere or ether.

Since antenna I is short with respect to a wave length it will have alow radiation resistance and high capacitive reactance and hence wouldbe inefficient. The resonator formed by plates 5 and 6 and rods I doesnot fully overcome these deficiencies. In order to load this antennaproperly to achieve the desired compensation a second or inner cage isprovided by a plurality of rod-s 8, arranged on a smaller diameter andconcentric with circle of rods I, extending between plates 5 and 6. Amovably adjustable plate 9 is provided mounted on rods 8. This plate maybe adjusted to provide the desired resonance loading for the dipole I tocompensate the capacitive reactance and obtain the desired radiationefiiciency. Plate 9 and rods 8 together with plate 5 form a secondresonator about dipole I. When plate 9 is properly adjusted tocompensate the capacitive reactance of dipole I, the spacing betweenplates 9 and 5 will be less than \/2 at the mid-operating frequency sothat the resonator action will be inductive. Here again the spacebetween adjacent rods 8 and plates 9 and 5 bounds effectively a short.

section of wave guide. This wave guide will have a filtering actiontending to reduce. the amount of energy radiated from the resonator butsince the length of wave guide is very short as determined by diameterof rods 8 this eifect will be negligible. After adjustment of thisresonator structure there may still be a slight mismatch between theentire antenna assembly and transmission line I. In this case a matchingimpedance may be bridged on the line and may be housed for examplewithin the rotary coupler 3. Certain of the rods 8 may be made in theform of hollow conductors as indicated at I0, II, I2 and I3. These mayserve as coaxial transmission lines for feeding respective antenna unitsI4, I5, I6 and II, Figs. 2 and 3, which may be mounted between therespective hollow conductors and the next adjacent rods 8. Sep-, aratefeed lines I8, I9, 20 and 2! may be provided each of substantially equallength to supply to these antenna units energy in cophasal relationcoming in over a common feed line 22. The structure so far describedwill provide a rotatable figure-of-eight and omnidirectional patternwhich will be generally horizontally polarized. However, due to theresonator action itself a certain amount of vertical polarization may beradiated from the structure due to the radiation about the upper andlower ends of the resonator cage. An understanding of how this verticalpolarization arises and how it may be compensated may be had byreference to the diagrammatic illustrations of Figs. 4, 5 and 6.

Turning first to Fig. 4, the radiation coming from the resonator formedby plates 5 and E and rods 7, will be in the general form shown by lines23 and lines 24 of Fig. 4. It will be seen that the radiation lines ofelectric force which close around the portion of the resonator definedby rods I are purely horizontally polarized. However, some of the energylines as shown at 24 will close over the ends of the resonator structureand these lines since they are in the vertical plane or have componentsin this plane will produce accompanying vertical polarizationcomponents. It has been found that by adding extensions to the mainresonator cage as indicated at 25 of Fig. 5 this accompanying verticallypolarized energy can be reduced to an inconsequential value. It isbelieved that this is caused as illustrated in Fig. 5 by forming such anextension so that additional lines of force tend to terminate around thecylindrical resonator. Since the radiation from the antenna is verylarge this energy will be greatly attenuated as it travels up or downthe extensions so that any line of force on the end plates will producenegligible vertically polarized components.

Fig. 6 illustrates the effect of the lines of electric field from theomnidirectional loop 26 shown generalized instead of by separateconductors I 4-II as in Figs. 1-3. So long as the loop elements are madeso short that energy fed thereto is substantially constant throughoutthe length of these radiators substantially pure horizontal polarizedenergy will be radiated therefrom. As long as the conditions describedobtain with respect to the omnidirectional radiator this radiator may bemounted anywhere about the dipole either within the resonator cages oroutside thereof. Should there exist any vertically polarized componentsin the omnidirectional radiator it is desirable further that thisradiator be mounted within the cage resonator structure so that suchcomponents may be effectively filtered out.

Turning back to Fig. 1, these extensions are illustrated as plates 21and 28 interconnected with plates 5 and 6 respectively by means of rods29 and 312. The entire antenna assembly may be mounted directly on theground or on any suitable support as indicated at 3|.

While Fig. 1 gives an idea of a structure in accordance with ourinvention, a better understanding of the feeding of antenna units I4,I5, I 6 and Il may be had by reference to Figs. 2 and 3. In thesefigures it will be noted that the in-.

her conductors and transmissionlines I8, I9, 20 and 2I extend up throughrods Iii, II, I2 and I3 and out through openings therein across to thenext adjacent rods 8 of the assembly. In this manner the feeding can beaccomplished relatively simple. The pattern from the dipole I isindicated generally at 28a, Fig. 2, while the omfor operation in the 700to 800 megacycle range,

dmoie: antenna. I was made. substantially a. tenth. ofi'awa e lengthilong and was designed; for. 0911- pling toia motor for rotation; at.1800; R... R; M'. The inner: cagea was. made. of a. diameter; in. theonderof one halt-wavelength. at the: center irequency and the. spacingbetween rods: 15, 22 2-5. andiizfii wasmai-ile: the; order of one tenthwave length; Itlwill:be.recognizedi.thatronly'thedipole unit itselfineedibe. rotated, the; remaining part ofx'the. structure? being; fixed.lihis. arrangement was found. to. provide: as substantial impedance.match: betweenzthe; dipole; unit'and'a. 50; ohm. line feeding. thedipole; the normal radiation: resist-- 371138: at the: dipole: withoutthe load resonator cage being the order. of. 2-1-3 ohms; This: anJ-terma. was? found tosnoperate between. 7309 7.85. megacycles "with. no;greater: than. a. 2: '1 mismatch. oi: i'mpenance..v

As similar structure designed for: operating in. the very; high.frermenicy' range. between; 112: and:

1-18: megacycles and rotated. at. 18.00,: R; P; has

been; found. to provide. satisfactory-operating re sults showing. 3311iimprovement of: several. hon:- dred per cent over that: provided. bythe. conventional: antenna structures used for the omnirange beacons.

In Fig-.1 '7: is shown; a modification: of: the. arr-- tennawherein theouter" edge structure. comprises a cylindrical; sheet 3Zl:-,, terminatedat. its. ends: by plates; 32*, 33-. A plurality of slots 34 are.provided. in the, surface; of sheet 3L. These slots should. bedimensioned in accordance with. theopeningsbetween. the rods asdescribed in connection WithFig', 1 Extensions 35 and 36 may: be.provided above and below the resonator cage. structure, these;extensions. being shownas. extended: cylindrical. sheet portions. No.slots, need. be provided. in these extensions as their purpose: will. beiiulfilled. as well. without them. In. fact the.- extensions shown.in 1. could aswell. be, continuous. sheets, but the rod. construe-- tionis more convenient there. Moreover, the; openvconstructioni provideszalighter Weight structurelessz'sub ject'tozwinckpressures.

An inner cage structure is shown at 3'! which mayralso: be in; the. formof a cylindrical: sheet provided with slots 38'. The. adjustable wallportion may be in the form of a shorting plunger 39 which may beadjusted torender the desired portions of slots 38- effective. Thedipole radiator withincage 31 maybe the same as in Fig. 1, andtheorem-directional antenna may be-formed by conductors bridged acrosscertain of slots 38 and fed as in Fig. I. It Will be clear that ifdesired any combination of the rod construction Of Fig. 1 and thesheetconstruction of. Fig, 7 maybe-used.

While we have described above a particular example of our invention, itwill be readily recognized that many changes may be made therein withoutdeparting from the spirit of our invention. For example, various typesof omnidirectional radiators may be used with this system, it beingmerely necessary that proper horizontal polarization be maintained andthat the omnidirectional antenna is not mounted in such a position as tomake undesirable variations in the directive radiation pattern.Furthermore, the various wave lengths mentioned are not to be consideredto be limitations of our invention and the principles thereof areapplicable to any wave length. Moreover, a wide variation may beprovided in the length of the dipole radiator, it being borne in mindthat the efficiency of the antenna system and its radiation resistanceis to: be aadiustedi by means: oil: a. resonator having: dimensionssuitable to provide the necessamloadingz. Since: 2; short dipole;radiator has: a larger: capacity reactanca, the resonator structune:will generally be.- predominantly; inductive; to compensate thecapacitive: reactance and; re;- duce the impedance to a real impedance.Any residual mismatch can beitaken. care of by any known. typeoirimpedancer-matchingv device. Also the-dipoleneed not: be of thefolded type but: may: be-of any"desiredconstruction.

While. we: have described above theprinciples ofzour'inventioninconnectionwith specific. apiparatus, it is: to; be clearly" understood.-that. this description ismade: only by way of example and not; asza.limitation to; the scope of our invention.

We claim:

1-..A. radio antenna: assembly comprising; a radiating dipole antennaof. small length. relativeztoyhalf. a wavelength at theoperatingfrequency tnprovide a directive figure-of-eight pat-- tern, a; resonatorefiectively open to radiation abmitqonea periphery; thereof effectivelyenclosing. said". antenna, and an. omnidirectional antenna mountedsymmetrically about. said dipole an-- terma.

2;. Azradio antennaassemblyaccording to claim 1', wherein" said:resonator. comprises, a pair of plates; having conductive.- surfaces,spaced on oppositeasides of saiddipole, and. aplurality of con-(hIBtiVGj-z rods perpendicular to; the planeof-polari'zation of said:dipole, spaced around the. dipole andlv connected. to. said: plates, andsaid omnidiitectionalantenna. comprises, radiating elements.

symmetrically spaced around said dipole and connected: forcophasal;energization.

3: Alradioiantenna.assemblyaccordingto claim 1-,. wherein said.resonator comprises a pair of plates. having conrluctivezsurfaces,spaced. on op-- posite'sides'of said dipole, and a-cylinder with aphirality'ofspaced slots:p.erpendicular to the plane of polarization of.said. dipole, spaced around. the. dipole. and connected to said plates,and said? omnidirectional; antenna.- comprises radiatingelements-symmetrically spaced; around saidldipole andiconnected for'cophasal energizetiona 4'. radio antenna assembly accordingtto claim 1,further comprising an: extension at one end.

of said resonator for attenuating any component radiation energypolarized perpendicularlyto the". plane ofi polarizai'ii'on ofsaidradiator;

e. A radio: antenna according to claim 4, fur-- ther comprising anextension at the other end, of said resonator for attenuating saidperpendicular' polarized component.

6. A radio antenna assembly comprising 2. (ii-- poleradiator havinganoverall length short with respect to a quarterwave length at theoperating frequency, a pair of conductive plates spaced apart onopposite sides of and substantially concentric with the center of saiddipole, conductive means interconnecting said plates and providingregularly spaced conductive openings extending substantiallyperpendicularly to said plates, said plates and conductive means forminga resonator cage substantially matching the impedance of said antenna tothe radiation space at said operating frequency, a plurality ofradiators at regularly spaced intervals extending between adjacent oneof said conductive means, and means for cophasally exciting saidradiators.

'7. A radio antenna assembly according to claim 6, wherein saidconductive means comprises a 7 cylinder provided with a plurality ofspaced slots therein.

8. A radio antenna assembly according to claim 6, wherein saidconductive means comprises a plurality of spaced rods, arranged in acircular pattern and spaced apart to provide said conductive openings.

9. An antenna assembly for providing a rotatable unidirectionalradiation pattern comprising a rotatable dipole antenna to provide adirective radiation pattern, a resonator comprising a pair of plates anda set of rods interconnecting said plates forming a resonator forimpedance loading of said dipole, a plurality of antenna elements,symmetrically mounted about said resonator structure and said dipole toprovide an omnidirectional radiation pattern, and means for supplyingradio frequency energy to said dipole and said antenna element.

10. An antenna assembly comprising a first cage structure including fourplates mounted in parallel planes and spaced apart along a given axis,and a plurality of rods regularly spaced apart at spacings small withrespect to a half wave length and arranged on a circle of a givendiameter concentric with said axis, said rods extending between adjacentones of said plates and being fastened thereto; a second cage structurewithin said first cage structure mounted between the center two of saidfour plates, said second cage structure comprising a plurality of rodsmounted between said plates on a periphery of diameter less than saiddiameter, and a movable plate mounted on said rods for adjustablepositioning therealong, a dipole radiator rotatably mounted on one ofsaid two plates within said second cage structure, energizing means forsupplying radio frequency energy to said dipole radiiator, four radiatorelements mounted between adjacent rods of said second cage structure andregularly spaced from one another, one end of each radiator beingconnected to respective of said rods, the rods adjacent similar ends ofsaid radiators being made hollow, energizing conductors within saidhollow rods and connected to the respective other ends of saidradiators, and a common feeding conductor coupled to the free ends ofsaid conductors, to supply energy to said radiator elements cophasally.

11. An antenna assembly according to claim 10,

further comprising an extension on at least the upper end of said firstcage structure for attenuating any component radiation energy polarizedperpendicularly to the plane of polarization of said radiator.

12. A radio antenna assembly for radiating horizontally polarised wavescomprising a substantially cylindrical radiant energy emitting resonatorfor radiating energy substantially horizontally polarised and anextension at one end of said resonator for attenuating any verticallypolarised component radiation energy from said resonator, said extensionhaving substantially the same cross-sectional dimensions as saidresonator and being electrically connected thereto.

13. A radio antenna according to claim 12, fur-v ther comprising anextension at the other end of said resonator of substantially the samecrosssectional configuration for further attenuating saidperpendicularly polarised components.

14. A radio antenna assembly comprising a directive radiator of smalldimensions relative to a half Wavelength for radiating a figure-of-eightpattern of plane polarized energy, a resonator effectively open toradiation about one periphery thereof effectively enclosing saiddirective radiator and forming effectively a polarization filter aboutsaid open periphery, an extension at one end of said resonator forattenuating any component radiation energy polarized perpendicularly tothe plane of polarization of said radiator, and an inner resonator opento radiation about its periphery and adjustable to compensate theinherent capacitive reactance of said radiator.

15. A radio antenna assembly comprising a directive radiator of smalldimensions relative to a half wavelength for radiating a figure-of-eightpattern of plane polarized energy, a resonator efiectively open toradiation about one periphery thereof effectively enclosing saiddirective radiator and forming efiectively a polarization filter aboutsaid open periphery, an extension at one end of said resonator forattenuating any component radiation energy polarized perpendicularly tothe plane of polarization of said directive radiator, and anomnidirectional radiator for radiat ing energy plane polarized in thesame plane as said directive radiator, said omnidirectional radiatorcomprising short radiating elements mounted symmetrically about saiddirective radiator.

FRANK J. LUNDBURG. FRANCIS X. BUCHER.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain June 11, 1943

